Cyndi Lauper fluffed her performance of the US national anthem this weekend, as part of a 9/11 memorial at the US Open. The 58-year-old singer was performing The Star-Spangled Banner following a moment of silence for victims of the terrorist attacks in the US – but failed to sing the words correctly.

"O'er the ramparts we watched," Lauper sang, "as our flag was still streaming." While this sounds perfectly plausible, the real lyrics use more complicated grammar – and a fancier adverb: "O'er the ramparts we watched, were so gallantly streaming."

A true professional, Lauper gave no indication she had mixed up her lines. Singing through to the end, she later admitted the mistake on Twitter. "I got choked up in the middle remembering 9/11," she wrote. "I hope I didn't mess up too bad. I wanted it to be comforting."

Lauper is not the first singer to confuse the words to The Star-Spangled Banner. There seems to be something confounding about Francis Scott Key's 1814 poem. Earlier this year, Christina Aguilera got the same lines wrong during a rendition at the Super Bowl. Before a television audience of more than 100 million people, she sang about gleaming twilight instead of gallant streaming. "I can only hope that everyone could feel my love for this country and that the true spirit of its anthem still came through," Aguilera said later.